C3 and systemic lupus erythematosus: Serum PGLYRP2 was negatively correlated with C3 level (r = 0.5113, P < 0.01), C4 level (r = 0.4358, P < 0.01), and eGFR (r = 0.4587, P < 0.01); positively correlated with 24-h urine protein level (r = 0.5226, P < 0.01); negatively correlated with IgA (r = 0.4046, P < 0.01) (Fig. 3B) in SLE patients.